Eu(III) and Cm(III) sorption onto synthetic and natural kaolinite (St. Austell, UK) were studied by batch sorption experiments and time-resolved laser fluorescence spectroscopy (TRLFS). All investigations were performed under argon atmosphere (O2<1 ppm). 0.1 M NaClO4 and 0.25 g/L kaolinite were used as electrolyte and solid concentrations, respectively, throughout the study. Batch sorption experiments were performed with Eu(III), a homologue to trivalent actinides at three different metal ion concentrations between 6.6×10−8 and 6.6×10−6 M. pH-dependent sorption was found to be congruent for the two lowest Eu(III) concentrations (6.6×10−8 and 6.6×10−7 M) while a shift of the sorption distribution coefficient, Kd, to higher pH values was observed for the highest metal ion concentration (6.6×10−6 M). Furthermore, the natural kaolinite showed higher uptake of Eu(III) for the lowest metal ion concentration at pH<5 as compared to the synthetic product. This difference is believed to arise from a higher amount of Eu(III) being sorbed as outer-sphere species on the natural kaolinite due to its negative surface charge being higher than that of the synthetic mineral. The spectroscopic investigations were performed with 2×10−7 M Cm(III) as a luminescent probe. Four single component spectra could be extracted from the recorded emission spectra for both the synthetic and the natural kaolinite, with peak positions in average at 598.8, 602.7, 607.4 and 611.0 nm. The three first emission peaks appearing between pH 5 and 13 were assigned to three inner-sphere Cm-complexes. The fourth emission peak appearing in the alkaline pH range (>9) is assumed to be a result of Cm(III) incorporation by a surface precipitate of hitherto unknown composition.